]> git.ipfire.org Git - thirdparty/postgresql.git/commit
postgres_fdw: Avoid "cursor can only scan forward" error.
authorEtsuro Fujita <efujita@postgresql.org>
Fri, 19 Jul 2024 04:15:03 +0000 (13:15 +0900)
committerEtsuro Fujita <efujita@postgresql.org>
Fri, 19 Jul 2024 04:15:03 +0000 (13:15 +0900)
commitd97f2ee50e49046a984665fb72fa14a06bd58435
tree97606a4356090e8f76924015e4860d9fc1e6c228
parent9cd365f28f31dc8ea9d8c10ec7abd658aa29fcf5
postgres_fdw: Avoid "cursor can only scan forward" error.

Commit d844cd75a disallowed rewind in a non-scrollable cursor to resolve
anomalies arising from such a cursor operation.  However, this failed to
take into account the assumption in postgres_fdw that when rescanning a
foreign relation, it can rewind the cursor created for scanning the
foreign relation without specifying the SCROLL option, regardless of its
scrollability, causing this error when it tried to do such a rewind in a
non-scrollable cursor.  Fix by modifying postgres_fdw to instead
recreate the cursor, regardless of its scrollability, when rescanning
the foreign relation.  (If we had a way to check its scrollability, we
could improve this by rewinding it if it is scrollable and recreating it
if not, but we do not have it, so this commit modifies it to recreate it
in any case.)

Per bug #17889 from Eric Cyr.  Devrim Gunduz also reported this problem.
Back-patch to v15 where that commit enforced the prohibition.

Reviewed by Tom Lane.

Discussion: https://postgr.es/m/17889-e8c39a251d258dda%40postgresql.org
Discussion: https://postgr.es/m/b415ac3255f8352d1ea921cf3b7ba39e0587768a.camel%40gunduz.org
contrib/postgres_fdw/expected/postgres_fdw.out
contrib/postgres_fdw/postgres_fdw.c
contrib/postgres_fdw/sql/postgres_fdw.sql